荞麦皮生物吸附去除水中Pb^(2+)的性能研究

Investigation of Biosorption of Lead(Ⅱ) from Aqueous Solution Using Buckwheat(Fagopyrum esculentum Moench) Husk

农业废弃物荞麦皮用作廉价生物吸附材料,研究其吸附去除水中Pb^(2+)的性能和影响因素.采用间歇实验考察了p H、吸附剂用量、粒径、Pb^(2+)初始浓度、吸附时间和温度对荞麦皮吸附去除水中Pb^(2+)的影响.结果显示:p H在2.0~5.5之间,荞麦皮对Pb^(2+)的吸附量随p H增加不断增大,然后趋于恒定;吸附容量随荞麦皮粒径和用量的增大在减小.荞麦皮吸附Pb^(2+)的过程相对较快,5 h基本达到平衡,吸附动力学过程可用新建立的QS模型描述.吸附等温线分别采用Langmuir,Freundlich,Dubinin-Radushkevich和Temkin方程进行拟合,结果发现它们都能较好的描述等温吸附数据,其中Langmuir等温线方程拟合最好,45℃时对应的最大吸附量qmax为31.78 mg/g.Pb^(2+)在荞麦皮上的吸附过程的自由能的变化值ΔG约为-22.01(±0.65)k J/mol,Dubinin-Radushkevich平均吸附能E约为10.43(±0.45)k J/mol,且受温度影响较小,表明该吸附过程是一个自发的离子交换化学吸附.此外,采用酸和碱对荞麦皮进行预处理,结果显示酸处理会降低荞麦皮对Pb^(2+)的吸附,而碱处理能稍微提高其对Pb^(2+)的吸附.本研究结果表明荞麦皮可作为廉价、绿色吸附材料用于水中Pb^(2+)的吸附去除.

Buckwheat husk,an agricultural waste,is used as a potential biosorbent to remove lead ions from aqueous solution. The batch experiments are conducted to investigate the influence of solution p H,adsorbent dosage,particle size of sorbent,initial concentration of lead ion,reaction time and temperature on the adsorption capacity of buckwheat husk to lead ion. Furthermore,isotherms,kinetics and thermodynamics of the biosorption are explored as well. Experimental results show that the adsorption capacity of buckwheat husk to lead ion increases with the increase of solution p H values from 2. 0 to 5. 5,and increases with increasing adsorbent concentration,but decreases with an increase in particle size of adsorbent. Adsorption of lead on buckwheat is a relatively fast process with a shorter equilibration time about 5 hours. The adsorption kinetic data can be fitted by a new developed model,which is based on the concept of a quick equilibrium adsorption followed by a slow adsorption process. The adsorption isotherms are analyzed by using Langmuir, Freundlich, Dubinin-Radushkevich and Temkin isotherm equations. Results indicate that all of them can describe equilibrium data reasonable,but the Langmuir equation gives the best results according to the corresponding values of R2. The maximum adsorption capacity from the Langmuir isotherm is found to be about 31.78 mg/g at 45℃. The changes in Gibbs free energy( ΔG) and the mean free energy( E) calculated from Dubinin-Radushkevick equation for adsorption of lead ion on buckwheat husk are about-22. 01( ± 0. 65) k J/mol and 10. 43( ± 0. 45) k J/mol,respectively. The values of ΔG and E further indicate that the adsorption of lead ions on buckwheat is a spontaneously ion-exchange chemical sorption. In addition,the effect of acid-basic pretreatment on lead adsorption by buckwheat husk is also examined. Results have revealed that the acid treatment decreases the adsorption of lead ions,while the basic treatment slightly enhances the adsorption of lead ions. This study suggests that the buckwheat husk can be used as a low cost and environmentally-friendly adsorption material for the removal of lead from water.